CN112639602B

CN112639602B - Backboard with hexagonal and triangular electrodes

Info

Publication number: CN112639602B
Application number: CN201980055507.8A
Authority: CN
Inventors: A·蔡; I·法兰西; C·维沙尼; D·辛汤摩斯基; R·J·小保利尼
Original assignee: Nucleoprotein Co ltd
Current assignee: Nuclera Ltd
Priority date: 2018-09-17
Filing date: 2019-09-17
Publication date: 2024-03-29
Anticipated expiration: 2039-09-17
Also published as: EP3853662A1; WO2020060960A1; TW202020539A; US20200089035A1; TWI724549B; EP3853662A4; EP3853662B1; CN112639602A; US11353759B2

Abstract

The active matrix back plate comprises an array of hexagonal electrodes or an array of triangular electrodes. Since the backplate design distributes the wire grid lines along the periphery of the electrodes, less cross-talk with the electrode surface occurs. The disclosed design simplifies the construction and control of the electrodes and improves the regularity of the electric field over the electrodes. Such back plate electrode designs are particularly useful in electrowetting on dielectric (EWoD) devices and electrophoretic displays (EPDs).

Description

Backboard with hexagonal and triangular electrodes

Technical Field

The present application claims priority from U.S. provisional patent application No. 62/732,421 filed on 2018, 9, 17. All references, patents and patent applications disclosed herein are incorporated by reference in their entirety.

The present invention relates to backplanes for electro-optic displays. More particularly, it relates to non-conventional pixel shapes such as hexagons or triangles. Many displays (LCDs and electrophoretic displays) use an array of electrodes to present various colored pixels that are perceived by a viewer as an image. Such pixel arrays have traditionally used rectangular or square electrodes, sometimes with edge structures. In this case, each electrode has four nearest neighboring electrodes joined by edges. Because of the array structure, the pixels can be addressed quickly and independently using the scan lines and gate lines and a coordinated controller. Similar structures may be used for non-display purposes such as particle sensing and electrowetting on dielectric (EWoD).

Background

As the term "electro-optic" is applied to a material or display, it is used herein in its conventional sense in the imaging arts to refer to a material having first and second display states that differ in at least one optical property, the material being changed from its first display state to its second display state by application of an electric field to the material. Although the optical property is typically a color perceptible to the human eye, it may be another optical property, such as light transmission, reflection, luminescence, or, in the case of a display for machine reading, a false color in the sense of a change in reflectivity of electromagnetic wavelengths outside the visible range. Although the present application refers to devices as electro-optic devices, it is generally understood that the same structure may be used for non-optical, i.e., non-display applications, such as particle sensing or electrowetting on dielectric (EWoD).

The term "gray state" is used herein in its conventional sense in the imaging arts to refer to a state intermediate between the two extreme optical states of a pixel, but does not necessarily mean a black-and-white transition between the two extreme states. For example, several of the Iying patents and published applications referred to hereinafter describe electrophoretic displays in which the extreme states are white and dark blue such that the intermediate "gray state" is effectively pale blue. In fact, as already mentioned, the change in optical state may not be a color change at all. The terms "black" and "white" may be used hereinafter to refer to the two extreme optical states of the display and should be understood to generally include extreme optical states that are not strictly black and white, such as the white and deep blue states mentioned above. The term "monochrome" may be used hereinafter to refer to a driving scheme that drives a pixel to only its two extreme optical states, without an intermediate gray state.

The terms "bistable" and "bistable" are used herein in their conventional sense in the art to refer to displays comprising display elements having first and second display states, at least one optical characteristic of which differs such that after any given element is driven to assume its first or second display state with an addressing pulse of finite duration, that state will last at least several times (e.g. at least 4 times) the minimum duration of the addressing pulse required to change the state of that display element after the addressing pulse has terminated. In published U.S. patent application No. 2002/0180687 (see also corresponding international application publication No. WO 02/079869), some particle-based electrophoretic displays supporting gray scale may be stable not only in their extreme black and white states, but also in their intermediate gray states, and some other types of electro-optic displays. This type of display is properly referred to as "multi-stable" rather than bistable, but for convenience the term "bistable" may be used herein to encompass both bistable and multi-stable displays.

The term "impulse" is used herein in its conventional sense, i.e. the integration of voltage with respect to time. However, some bistable electro-optic media are used as charge converters, and for such media an alternative definition of impulse, i.e. the integration of current with respect to time (which is equal to the total charge applied), may be used. Depending on whether the medium is used as a voltage-to-time impulse converter or as a charge impulse converter, the appropriate impulse definition should be used.

Numerous patents and applications assigned to or on behalf of the institute of technology (MIT) and the company eikon are recently disclosed, describing encapsulated electrophoretic media. Such encapsulated media comprise a plurality of capsules, each capsule itself comprising an internal phase and a wall surrounding the internal phase, wherein the internal phase contains electrophoretically-mobile particles suspended in a fluid suspension medium. Typically, these capsules themselves are held in a polymeric binder to form a coherent layer between the two electrodes. The techniques described in these patents and applications include:

(a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Pat. nos. 7,002,728 and 7,679,814;

(b) A capsule body, an adhesive and a packaging process; see, for example, U.S. patent nos. 6,922,276 and 7,411,719;

(c) Films and subassemblies comprising electro-optic materials; see, for example, U.S. Pat. nos. 6,982,178 and 7,839,564;

(d) Backsheets, adhesive layers, and other auxiliary layers and methods for use in displays; see, for example, U.S. patent No. D485,294; 6,124,851; 6,130,773; the patent is a patent with the functions of 6,177,921, 5235, 6,177,921, 5235, 20135, 20120135, 201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201201,. 1,099,207 B1 and 1,145,072 B1;

(e) Color formation and color adjustment; see, for example, U.S. patent nos. 7,075,502 and 7,839,564;

(f) A method for driving a display; see, for example, U.S. Pat. nos. 5,930,026; 6,445,489; 6,504,524; 6,512,354, 6,531,997, 6,753,999, 8625, 6,900,851, 6,995,550, 7,012,600, 7,023,420, 7,034,783, 7,116,466, 7,119,772, 7,193,625, 7,202,847, 7,259,744, 7,304,787, 7,312,794, 7,327,511, 7,453,445, 7,492,339, 7,528,822, 7,545,358, 7,583,251, 7,602,374, 7,612,760, 7,679,599, 7,688,297, 7,729,039, 7,733,311, 7,733,335, 7,787,169, 7,952,557, 7,956,841, 7,999,787, 8,077,141, 8,125,501, 8,139,050, 8,174,490, 8,289,250, 8,300,006, 8,305,341, 8,314,784, 8,373,649, 8,384,658, 8,558,783, 8,558,785, 8,593,396, and 8,928,562, as well as U.S. patent application publication nos. 2003/0102858, 2005/0253777, 2007/0091418, 2007/0103427, 2008/0024429, 2008/00282, 2008/0174, 2008/0291129, 2009/4651, 01723, 2009/01768, 2009/550221, 2009/27931, 2012012012012012012012012012012012012012012012012012012012012012012012012012012012012012012012012012012012012012012015, 2012012012012012012012012012012012015, 2012012012012015, 2012012012015, 2012012015, 2012015, 2012012015, 2015, 2012015, 2015;

(g) Application of the display; see, e.g., U.S. patent nos. 6,118,426, 6,473,072, 6,704,133, 6,710,540, 6,738,050, 6,825,829, 7,030,854, 7,119,759, 7,312,784, and 8,009,348, 7,705,824, 8,064,962, and 8,553,012, and U.S. patent application publication nos. 2002/0090980, 2004/019681, and 2007/0285385, and international application publication No. WO 00/36560; and

(h) Non-electrophoretic displays, as described in U.S. Pat. Nos. 6,241,921, 6,950,220, 7,420,549, 8,319,759, and 8,994,705, and U.S. patent application publication Nos. 2012/0293858.

The present invention provides an efficient design for a pixel array having a non-conventional shape that can employ conventional scan and gate lines, controllers, shift registers, and the like.

Disclosure of Invention

The invention provides a back plate having an array of hexagonal electrodes or an array of triangular electrodes. Since the backplate design distributes the wire grid lines along the periphery of the electrodes, less cross-talk with the electrode surface occurs. These designs simplify the construction and control of the electrodes and improve the regularity of the electric field over the electrodes. Such electrode designs may be particularly useful in particle sensing and EWoD applications, but there is no reason why these designs cannot be used for more traditional displays, such as LCD displays or electrophoretic displays (EPDs).

The disclosed backplane electrode structures are advantageous in that they are easy to couple to standard controllers and can result in simple pin assignments for plug and play with existing ecosystems. This reduces the complexity of the substrate and the interface with the printed circuit board, thereby reducing costs.

In one aspect, the present invention provides a pixel electrode back plate including a plurality of scan lines, a plurality of gate lines, a plurality of storage capacitors, a plurality of thin film transistors, and a plurality of hexagonal electrodes. Typically, the storage capacitor is greater than 0.5 pF. In the present invention, the hexagonal electrodes are arranged in a honeycomb structure, and the voltage potential of each hexagonal electrode can be controlled using only one scan line and only one gate line. In some embodiments, a plurality of scan lines are coupled to the scan controller, and a plurality of gate lines are coupled to the gate controller. In some embodiments, the gate lines are routed parallel to the edges of the hexagonal electrodes.

In another aspect, the present invention provides a pixel electrode back plate including a plurality of scan lines, a plurality of gate lines, a plurality of storage capacitors, a plurality of thin film transistors, and a plurality of triangular electrodes. Typically, the storage capacitor is greater than 0.5 pF. In the present invention, two or four triangular electrodes are arranged in a square, and the voltage potential of each triangular electrode can be controlled with only one scan line and only one gate line. In some embodiments, a plurality of scan lines are coupled to the scan controller, and a plurality of gate lines are coupled to the gate controller. In some embodiments, the gate lines are routed parallel to the edges of the triangular electrodes. In some embodiments, the scan lines are routed parallel to the edges of the triangular electrodes.

The functionality of the back plate electrode may be extended by arranging a dielectric layer over the pixel electrode and a hydrophobic layer over the dielectric layer. Such a coated pixel electrode back-sheet may be incorporated into a microfluidic device by adding a light transmissive electrode and a spacer arranged between the pixel electrode back-sheet and the light transmissive electrode.

In other embodiments, the backplane electrode may be the basis for controlling an electrophoretic display (EPD) by adding a light transmissive electrode and disposing an electrophoretic medium (typically charged particles in a nonpolar solvent) between the backplane electrode and the light transmissive electrode.

Drawings

Fig. 1 shows a plurality of hexagonal electrodes arranged in a honeycomb structure. The present invention provides for easy fabrication of such an array while providing for simple individual control of each hexagonal shaped pixel by the scan lines and gate lines.

Fig. 2 shows driving details of a hexagonal array, including gate lines (G _n ) Scanning line (S) _n ) Thin film transistors and storage capacitors.

FIG. 3 illustrates an embodiment of a pixel electronics for a hexagonal electrode;

fig. 4A and 4B illustrate an embodiment of a backplate using the hexagonal electrode architecture of the present invention. The embodiment of fig. 4A includes 217×164= 35,588 pixel electrodes, a gate controller having 825 channel output modes, and a data controller having 800 channel output modes.

Fig. 5 shows a first embodiment of an array of triangular electrodes, where electrodes a and B form a square.

Fig. 6 shows a second embodiment of an array of triangular electrodes, where electrodes A, B, C and D form squares.

Fig. 7A and 7B illustrate an embodiment of a backplate using the triangular electrode architecture of the present invention. The embodiment of fig. 7A includes 374×163= 60,962 pixel electrodes, a gate controller having 825 channel output modes, and a data controller having 800 channel output modes.

Fig. 8 shows an embodiment of a back plate using the triangular electrode architecture of the present invention.

Fig. 9 depicts the movement of aqueous phase droplets between adjacent electrodes by providing different charge states on adjacent electrodes. In fig. 9, negative charges are induced in the liquid at the liquid/dielectric interface above the (lower) electrode receiving the AC signal, while positive charges are induced when a negative voltage is applied to the opposite (upper) electrode. (the figure shows the moment the leftmost electrode is positively charged during the AC cycle.) as shown in fig. 9, the pixel always has a charge opposite to the induced charge at the droplet interface.

Fig. 10 shows a TFT architecture for multiple boost electrodes of an EWoD device of the present invention.

Fig. 11 is a general diagram of an electrophoretic medium suitable for use in the back-sheet of the present invention.

Detailed Description

The present invention provides arrays of hexagonal and triangular electrodes that can be individually addressed by conventional scan/gate driving. Such arrays may be used to create displays, such as Liquid Crystal Displays (LCDs) or electrophoretic displays (EPDs). Such arrays may also be useful in non-display applications, such as particle (e.g., photon) sensors or electrowetting on dielectric (EWoD), which may be used in microfluidic applications, such as lab-on-a-chip experiments.

Creating a digital picture requires the ability to quickly address individual spatial elements (pixels). In some cases, each pixel is its own color source (e.g., a full color electrophoretic display as described in U.S. patent No. 9,921,451), and in other cases several sub-pixels cooperate to provide the pixel with a series of color views. Although each pixel may be wired to control voltage states individually, it is more common to provide an array of nonlinear elements (e.g., transistors or diodes), with at least one nonlinear element being associated with each pixel (or subpixel) to produce an "active matrix" display. The addressing electrode or pixel electrode that addresses a pixel is connected to an appropriate voltage source through an associated nonlinear element. Typically, when the nonlinear element is a transistor, the pixel electrode is connected to the drain of the transistor, and such an arrangement will be adopted in the following description, but this is arbitrary in nature, and the pixel electrode may be connected to the source of the transistor. Conventionally, in high resolution arrays, pixels are arranged in a two-dimensional array of rows and columns such that any particular pixel is uniquely defined by the intersection of a specified row and a specified column. The sources of all transistors in each column are connected to a single column electrode, while the gates of all transistors in each row are connected to a single row electrode; also, the allocation of sources to rows and gates to columns is conventional but arbitrary in nature and can be reversed if desired. The row electrodes are connected to a row driver which essentially ensures that only one row is selected at any given time, i.e. that a voltage is applied to the selected row electrode to ensure that all transistors in the selected row are conductive, while a voltage is applied to all other rows to ensure that all transistors in these unselected rows remain non-conductive. The column electrodes are connected to a column driver which applies voltages to the respective column electrodes selected to drive the pixels in the selected row to their desired optical states. (the voltages described above are relative to a common front electrode that is typically disposed on opposite sides of the non-linear array of electro-optic medium and extends across the entire display.) after a pre-selected interval called the "line addressing time", the selected row is deselected, the next row is selected, and the voltage on the column driver is changed to write to the next row of the display. This process is repeated to write the entire display in a row-by-row fashion. (in this context, the gate lines are horizontal and the scan lines are vertical.) since the drive electronics are typically arranged in a matrix, the pixel electrodes coupled to the drive electronics are typically square or rectangular and are arranged in a rectangular array so as to maximize the area covered by the electrodes.

The process for manufacturing active matrix displays is well established. For example, various deposition and photolithography techniques can be used to fabricate thin film transistors. The transistor includes a gate electrode, an insulating dielectric layer, a semiconductor layer, and source and drain electrodes. Applying a voltage to the gate electrode provides an electric field across the dielectric layer, thereby greatly increasing the source-drain conductivity of the semiconductor layer. This variation allows conduction between the source and drain electrodes. Typically, the gate electrode, source electrode, and drain electrode are patterned. Typically, the semiconductor layer is also patterned to minimize stray conduction (i.e., cross-talk) between adjacent circuit elements.

Liquid crystal displays typically employ amorphous silicon ("a-Si"), thin film transistors ("TFTs") as switching devices for displaying pixels. Such TFTs typically have a bottom gate configuration. Within a pixel, a thin film capacitor typically holds the charge transferred by the switching TFT. An electrophoretic display may use similar TFTs with capacitors, although the function of the capacitors is different from that in a liquid crystal display; see the aforementioned co-pending application Ser. No. 09/565,413, and publications 2002/0106847 and 2002/0060321. Thin film transistors can be fabricated to provide high performance. However, the manufacturing process can result in significant costs.

In a TFT addressed array, the pixel electrodes are charged via TFTs during the on-line address time. During the line address time, the TFT is switched to an on state by changing the applied gate voltage. For example, for an n-type TFT, the gate voltage is switched to a "high" state to switch the TFT to an on state.

It should be understood that the back-plates described herein may be extended to electro-optic displays that include an electro-optic medium layer disposed on the back-plate and covering the pixel electrodes. Such an electro-optic display may use any of the types of electro-optic media previously discussed; for example, the electro-optic medium may be a liquid crystal, a rotating bi-color member or an electrochromic medium, or an electrophoretic medium, preferably an encapsulated electrophoretic medium. In some embodiments, when using an electrophoretic medium, a plurality of charged particles may move through a suspending fluid under the influence of an electric field. Such an electrophoretic display may have good brightness and contrast, wide viewing angle, state bistability, and low power consumption properties compared to a liquid crystal display.

The back-plates described herein may also be used for electrowetting on dielectric (EWoD). EWoD devices generally comprise a unit filled with oil and at least one aqueous droplet. The cell gap is typically in the range of 50 to 200 μm, but the gap may be larger. In a basic configuration, a plurality of push electrodes (pixels) are arranged on one substrate, and a single top electrode is arranged on the opposite surface. The cell also includes a hydrophobic coating on the surface in contact with the oil layer, and a dielectric layer between the propulsion electrode and the hydrophobic coating. (the upper substrate may also include a dielectric layer). The hydrophobic layer prevents the droplets from wetting the surface. When no voltage difference is applied between adjacent electrodes, the droplet will remain spherical to minimize contact with the hydrophobic surfaces (oil and hydrophobic layer). Since the droplets do not wet the surface, unless such behavior is required, they are less likely to contaminate the surface or interact with other droplets. By addressing the electrodes in the active matrix individually, the droplets of water can be moved, split and coalesced. Since water droplets are compatible with biomolecules, a micro-sample can be bioassay. Conventional rectangular arrays can limit the function of EWoD devices because the only choice is up/down/left/right, whereas the hexagonal electrode of the present invention has six nearest neighbors for more directions of movement and can apply force at 60 °, 120 ° and linearly.

Fig. 1 shows a top view of an array of hexagonal electrodes 100. Fig. 1 is arranged as a conventional honeycomb structure; however, other repeating structures are also possible. In addition, each hexagonal electrode need not be regular, as each side and each angle is the same.

Fig. 2 is a top view of drive electronics arranged for the hexagonal array of the present invention. As shown in fig. 2, each hexagonal electrode includes a Thin Film Transistor (TFT) 205 and a storage capacitor 210. As described above, the gate line 220 and the scan line 225 control the TFT 205. Notably, in the arrangement of the present invention, the gate lines run parallel to the perimeter of the hexagonal electrode. This allows each hexagonal electrode to be addressed by the gate lines and scan lines, as is commonly arranged in backplanes, and controlled by the gate controller and scan controller (see fig. 4A). Because the gate lines extend along the perimeter of the electrode (rather than underneath), the electric field across the electrode is more uniform across the electrode surface. This feature is particularly useful when the hexagonal electrode is large (i.e. on the order of 500 μm) and field non-uniformities can affect the performance of the device (i.e. stopping the droplet or displaying a wrong color).

The layout of the controller for the hexagonal array is shown in fig. 4A and 4B, which includes a gate controller and a scan controller. As shown in fig. 4A, using commercially available scan and gate controllers, more than 30000 electrodes can be arranged on a 5cm x 5cm back plate. See, e.g., MK Electric scan and gate controller. Using hexagonal electrodes of about 235 μm, while the spacing between the hexagonal electrodes is about 5 μm. Of course, the layout may be made larger or smaller, for example, the back plate may include 5,000 to 500,000 electrodes. In addition, the hexagonal electrode may be larger or smaller, i.e. between 50 μm and 1 mm. As shown in fig. 4B, the individual TFTs may be controlled with gate lines 420 and scan lines 425.

Fig. 5 and 6 show top views of an array of triangular electrodes. Fig. 5 shows a first embodiment of a triangular electrode, wherein two electrodes "a" and "B" create square features. Fig. 6 shows a second embodiment of a triangular electrode, wherein four electrodes "a", "B", "C" and "D" create square features. Other configurations of triangular electrodes may be fabricated to create squares. The arrays of fig. 5 and 6 may be used in both display and non-display applications, as in the hexagonal arrays described above.

Fig. 7A and 7B show top views of drive electronics arranged for a hexagonal array of the present invention. As shown in fig. 7B, each hexagonal electrode includes a TFT 705 and a storage capacitor 710. As described above, the gate line 720 and the scan line 725 control the TFT 705. It is noted that in the arrangement of the present invention, the gate lines and the scan lines run parallel to the perimeter of the triangular electrodes. This allows each triangular electrode to be addressed by a gate line and a scan line, as is typically arranged in a backplane, and controlled by a gate controller and a scan controller. Because the gate lines and scan lines extend along the perimeter of the electrode (rather than underneath), the electric field across the electrode is more uniform across the electrode surface. This feature is particularly useful when the triangular electrodes are large (i.e. on the order of 500 μm) and field inconsistencies can affect the performance of the device (i.e. stopping a droplet or displaying a wrong color).

Also shown in fig. 7A is a layout of the controller for the triangular array, which includes a gate controller and a scan controller. As shown in fig. 7A, using commercially available scan and gate controllers, more than 60000 electrodes can be arrayed on a 5cm x 5cm backplate. The use of triangular electrodes of about 150 μm is easy to achieve, whereas the spacing between the triangular electrodes is about 5 μm. Of course, the layout may be made larger or smaller, for example, the back plate may include 5,000 to 500,000 electrodes. In addition, the triangular electrodes may be larger or smaller, i.e. between 50 μm and 1 mm. An alternative arrangement of triangular electrodes is shown in fig. 8, where the gate lines 820 and scan lines 825 are perpendicular.

Of course, the arrangement of electrodes in the figures is exemplary, and the geometry of the pixel electrodes and/or gate lines and/or scan lines may be modified for a particular application or as the number of pixels is limited by the available scan controller or backplane dimensions. For example, the size of the pixel electrode may be reduced to increase a gap space between the electrode and the data line. In some other embodiments, the electrical characteristics of the material between the pixel electrode and the data line may be changed to reduce crosstalk. For example, the thickness of the insulating film between the pixel electrode and the data line adjacent thereto may be increased to reduce capacitive coupling.

In some embodiments, the back-plate of the present invention may be incorporated into an electrowetting on dielectric (EWoD) device that includes the back-plate of the present invention coupled to a light transmissive electrode and separated by a spacer. The basic operation of the EWoD device is shown in the cross-sectional view of fig. 9. EWoD 900 includes a cell filled with oil 902 and at least one aqueous droplet 904. The cell gap is defined by spacers (not shown) but is typically in the range of 50 to 200 μm, although the gap may be larger. In a basic configuration, as shown in fig. 9, a plurality of push electrodes 905 are arranged on one substrate, and a single light-transmitting top electrode 906 is arranged on the opposite surface. The cell further comprises a hydrophobic coating 907 on the surface in contact with the oil layer, and a dielectric layer 908 between the propulsion electrode 905 and the hydrophobic coating 907. (the upper substrate may also include a dielectric layer, but is not shown in FIG. 9). The hydrophobic layer prevents the droplets from wetting the surface. When no voltage difference is applied between adjacent electrodes, the droplet will remain spherical to minimize contact with the hydrophobic surfaces (oil and hydrophobic layer). Since the droplets do not wet the surface, unless such behavior is required, they are less likely to contaminate the surface or interact with other droplets.

Dielectric 908 must be thin enough and have a dielectric constant compatible with low voltage AC driving, such as is available from conventional image controllers for LCD displays. For example, the dielectric layer may comprise about 20-40nm of SiO capped with 200-400nm of plasma deposited silicon nitride ₂ A layer. Alternatively, the dielectric may comprise an atomic layer deposited Al having a thickness between 2 and 100nm, preferably between 20 and 60nm ₂ O ₃ . The TFT is constructed by creating alternating layers of differently doped a-Si structures and various electrode lines using methods known to those skilled in the art. The hydrophobic layer 907 may be composed of a material such as Teflon AF (Sigma-Aldrich of Milwaukee, wis.) and FlurorPel from Cytonix (Bei Ciwei mol, malay) ^TM A coating is configured which may be spin-coated on the dielectric layer 908.

Although it is possible to have a single layer for both dielectric and hydrophobic functions, such layers typically require a thick inorganic layer (to prevent pinholes), resulting in a low dielectric constant, thus requiring greater than 100V for droplet movement. To achieve low voltage actuation, it is preferable to have a thin inorganic layer to obtain high capacitance, and to have no pinholes, it is preferable to have a thin organic hydrophobic layer overlying it. By this combination, electrowetting operations can be performed at voltages in the range of +/-10 to +/-50V, which is within the range that conventional TFT arrays can provide.

When a voltage difference is applied between adjacent electrodes, the voltage on one electrode attracts opposite charges in the droplet at the dielectric-droplet interface and the droplet moves toward that electrode, as shown in fig. 2. The voltage required for acceptable droplet advancement depends on the characteristics of the dielectric and hydrophobic layers. AC driving is used to reduce degradation of droplets, dielectrics and electrodes due to various electrochemical effects. The operating frequency of EWoD may be in the range of 100 Hz to 1 MHz, but a lower frequency of 1 kHz or less is preferred for TFTs with limited operating speeds.

As shown in fig. 9, the top electrode 906 is a single conductive layer typically set to zero volts or a common voltage Value (VCOM) to account for the bias voltage on the push electrode 905 (see fig. 10) due to capacitive kickback of the TFT for switching the voltage on the electrode. The top electrode may also apply a square wave to increase the voltage across the liquid. Such an arrangement allows a lower drive voltage to be used for the drive electrode 905 connected to the TFT, since the top plate voltage 906 is additional to the voltage provided by the TFT.

As shown in fig. 10, the active matrix of the push electrodes (hexagonal or triangular or some other shape) may be arranged to be driven by data and gate (select) lines, much like the active matrix in a Liquid Crystal Display (LCD). Unlike LCDs, however, the storage capacitors of the present invention typically have much higher capacitance as required for electrophoretic displays and electrowetting devices on dielectric. For example, each storage capacitor in the backplate electrode array is typically greater than 0.1 pF (micro farads), such as greater than 0.5pF, such as greater than 1 pF, such as greater than 2 pF, such as greater than 5pF, such as greater than 10pF, such as greater than 50pF, such as greater than 100pF.

In EWoD applications, the gate (select) lines are scanned in a line-at-a-time addressing fashion, while the data lines carry voltages that will be transferred to the boost electrodes for electrowetting operations. If no movement is required, or if the droplet is to be moved away from the propulsion electrode, 0V is applied to the (non-target) propulsion electrode. If a droplet is to be moved towards the propulsion electrode, an AC voltage is applied to the (target) propulsion electrode.

An exemplary electrophoretic display (EPD) incorporating the pixel electrode backplane of the present invention is shown in fig. 11. Display 1100 generally includes a layer of electrophoretic material 1130 and at least two other layers 1110 and 1120 disposed on opposite sides of electrophoretic material 1130, at least one of which is a light transmissive electrode layer, for example, as shown by layer 1110 in fig. 11. The light transmissive electrode 1110 may be a transparent conductor, such as Indium Tin Oxide (ITO), which may be deposited on a transparent substrate (e.g., polyethylene terephthalate (PET)) in some cases. As shown in fig. 11, such EPD also includes a back plate 1150 that includes a plurality of drive electrodes 1153 and a substrate layer 1157. The electrophoretic material layer 1130 may include microcapsules 1133 that hold electrophoretic pigment particles 1135 and 1137 and a solvent, wherein the microcapsules 1133 are dispersed in a polymeric binder 1139. Nevertheless, it is understood that the electrophoretic medium (particles 1135 and 1137 and solvent) may be enclosed in microcells (microcups) or distributed in a polymer without surrounding microcapsules (e.g., the PDEPID design described above). Typically, the pigment particles 1137 and 1135 are controlled (displaced) by an electric field generated between the front electrode 1110 and the pixel electrode 1153. In many conventional EPDs, the electrical drive waveforms are transmitted to the pixel electrode 1153 via conductive traces (not shown) that are coupled to Thin Film Transistors (TFTs) that allow the pixel electrode to be addressed in a row-column addressing scheme. In some embodiments, the front electrode 1110 is only grounded and drives the image by providing positive and negative potentials to the individually addressable pixel electrodes 1153. In other embodiments, a potential may also be applied to front electrode 1110 to provide a greater variation in the field that may be provided between the front electrode and pixel electrode 1153.

From the foregoing, it can be seen that the present invention provides a back plate having an array of hexagonal or triangular electrodes. It will be apparent to those skilled in the art that many changes and modifications can be made to the specific embodiments of the invention described above without departing from the scope of the invention. The entire foregoing description is therefore to be construed in an illustrative and not a limiting sense.

Claims

1. An electrowetting-on-dielectric device comprising:

a pixel electrode backplane comprising:

a plurality of scan lines;

a plurality of gate lines;

a plurality of storage capacitors having a capacitance greater than 0.5 pF;

a plurality of thin film transistors; and

a plurality of hexagonal boost electrodes having a dielectric coating thereon and a first hydrophobic layer disposed thereon, the hexagonal boost electrodes being arranged in a honeycomb structure and each hexagonal boost electrode being operatively coupled to a storage capacitor and a thin film transistor, wherein a voltage potential of each hexagonal boost electrode is controllable with only one scan line and only one gate line, wherein the gate lines are routed parallel to edges of the hexagonal boost electrodes to make an electric field on the hexagonal boost electrodes more uniform across a surface of the hexagonal boost electrodes;

a light-transmitting electrode having a second hydrophobic layer disposed on the light-transmitting electrode; and

a spacer arranged between the pixel electrode back plate and the light-transmitting electrode,

wherein the electrowetting on dielectric device is configured to move aqueous droplets between hexagonal propelling electrodes.

2. The electrowetting device on dielectric of claim 1, wherein the plurality of scan lines are coupled to a scan controller and the plurality of gate lines are coupled to a gate controller.

3. An electrowetting device on dielectric according to claim 2, wherein the pixel electrode backplane is substantially rectangular in shape and the scan controller is arranged along a first edge of the pixel electrode backplane and the gate controller is arranged along a second edge of the pixel electrode backplane.

4. The electrowetting device on dielectric of claim 1, wherein the scan line is routed perpendicular to the gate line.

5. An electrowetting-on-dielectric device comprising:

a pixel electrode backplane comprising:

a plurality of scan lines;

a plurality of gate lines;

a plurality of storage capacitors having a capacitance greater than 0.5 pF;

a plurality of thin film transistors; and

a plurality of triangular boost electrodes having a dielectric coating thereon and a first hydrophobic layer disposed thereon, each triangular boost electrode operatively coupled to a storage capacitor and a thin film transistor, wherein four triangular boost electrodes are arranged in a square, and a voltage potential of each triangular boost electrode is controllable with only one scan line and only one gate line, wherein the gate lines are routed parallel to edges of the triangular boost electrodes to make an electric field on the triangular boost electrodes more uniform across a surface of the triangular boost electrodes;

wherein the electrowetting on dielectric device is configured to move aqueous droplets between triangular propulsion electrodes.

6. The electrowetting device on dielectric of claim 5, wherein the plurality of scan lines are coupled to a scan controller and the plurality of gate lines are coupled to a gate controller.

7. An electrowetting device on dielectric according to claim 6, wherein the pixel electrode backplane is substantially rectangular in shape and the scan controller is arranged along a first edge of the pixel electrode backplane and the gate controller is arranged along a second edge of the pixel electrode backplane.

8. The electrowetting device on dielectric of claim 5, wherein the scan line is routed perpendicular to the gate line.

9. The electrowetting device on dielectric of claim 5, wherein the scan line is routed parallel to an edge of the triangle-shaped boost electrode.